Restoring deteriorated pavements by “top coating” is a particularly attractive alternative for the various Departments of Transportation (DOT's) charged with maintaining the roads of their States because it offers a cost effective means to extend the service life of pavements. At a November 2010 Sponsors Meeting of the National Center for Asphalt Technology, several participants indicated that the majority of their budgets were spent on the rejuvenation and restoration of existing roads rather than on new construction, with many seeking to spend most of their budgets on top coating or thin coating projects as a cost effective way to restore or rejuvenate pavement. Residential driveways and commercial parking lots are also regularly top coated in order to extend their serviceable lives. Other than roads, driveways and parking lots, top coating is also used at airports on runways, taxiways, and desalting stations, not only to increase service life, but also as a means to increase resistance to jet fuel spills and aggressive desalting cocktails such as those containing glycols. Gilsonite is a natural asphalt material having a relatively high molecular weight and a much higher softening point (200-210° F.) than traditional asphalt (120-130° F.). These properties tend to make Gilsonite more resistant to solvent attack, but also result in a more brittle material which is prone to cracking under load, especially during periods of low temperature.
Additionally, conventional crude-based asphalt coating compositions can have relatively poor adhesion to the substrate in the presence of water. The eventual penetration of environmental water can reach the interface between the coating and the substrate surface, interfering with the bond between the coating and the substrate surface. This can result in flaking of the coating, exposing the substrate surface to weathering and/or solvent attack. In turn, such weathering and/or solvent attack, under load, can lead to substrate/pavement failures including flaked pavement, “raveling”, cracking, and potholes.
It would therefore be advantageous to have a coating material produced from a renewable source and that results in enhanced adhesion of the coating to the substrate surface, even in the presence of water. It would also be advantageous if such a coating demonstrated increased resistance to solvent attack.